Permeability,Solubility, and Diffusivity of Methane and Butane in Diphenylsiloxane-Dimethylsiloxane Copolymer Membranes

Permeation and sorption of methane and n-butane gases in polydimethylsiloxane (PDMS) and diphenylsiloxane-dimethylsiloxane (DPh-DM) block copolymer membranes were studied at room temperature and different upstream pressures. The membranes were prepared via room temperature vulcanization of vinyl terminated siloxanes through platinum catalyzed hydrosilylation reactions by mixing stoichiometric amounts of polymer, crosslinker, and catalyst, and casting of the mixture solutions with hexane. Composite membranes of polysiloxanes on a polyacrylonitrile microporous support were synthesized for permeation experiments and single layer dense films were used in sorption experiments. The effect of upstream pressure on permeability, solubility, and diffusivity of these membranes was evaluated. It was found that selectivity of the DPh-DM copolymer membrane for n-C₄H₁₀ relative to CH₄ was up to 19% higher than that in PDMS membrane. Both solubility and diffusivity selectivities had positive contributions in permselectivity improvement. The improvement in selectivity was attained with less than a 6% decrease in permeability of n-C₄H_10. Up to 11% improvement in selectivity was also obtained in mixed gas experiment.